Python3
This page tracks the progress of Python 3 effort porting for OpenStack.
Contents
Python 3
Why should OpenStack move to Python 3 right now?
- Python 3 is usually seen as the new Python version which breaks compatibility and raises new Unicode issues. Python 3 is much more than that. It’s a new clean language which has a more consistent syntax. It has many new features, not less than 15 new modules. Python 3 is already well supported by major Linux distributions, whereas Python 2.7 reached its end-of-life. Slowly, some bugs cannot be fixed in Python 2.7 anymore and are only fixed in the latest Python 3 release. Python 3 is now 5 years old and considered as a mature programming language.
Port Python 2 code to Python 3
OpenStack project chose to use the same code base for Python 2 and Python 3. The Six: Python 2 and 3 Compatibility Library helps to write code working on both versions.
References to port Python 2 code to Python 3
- Porting to Python 3 Book by Lennart Regebro, especially the Language differences and workarounds.
- HOWTO: Porting Python 2 Code to Python 3 by Brett Cannon
- Porting Python Code to 3.x
- python-incompatibility: Demonstrates incompatibilities between Python versions.
Common pitfalls
What is a string ?
You should definitely not talk about "strings" in your commit logs/reviews. In Python 2, a 'string' is bytes; in Python 3, it's a Unicode text string. The following code snippet may help in understanding the difference:
Python 2:
>>> type('foo') <type 'str'> >>> type(u'foo') <type 'unicode'> >>> type(b'foo') <type 'str'> >>> isinstance('foo', six.text_type) False >>> isinstance(u'foo', six.text_type) True >>> bytes is str True >>> b'foo'[0] 'f'
Python 3:
>>> type('foo') <class 'str'> >>> type(u'foo') <class 'str'> >>> type(b'foo') <class 'bytes'> >>> isinstance('foo', six.text_type) True >>> isinstance(b'foo', six.text_type) False >>> bytes is str False >>> b'foo'[0] 102
Python 3 of OpenStack Dependencies
Blocker Pointer: it's not yet possible to specify different list of dependencies for Python 2 and Python 3. For example, mox only works on Python 2, mox3 can be used on Python 3.
- Julien Danjou proposed to add requirements-py3.txt: openstack/requirements patch and openstack-dev/pbr patch
- An alternative is to support markers in requirements (in pip): pip issue: Support markers in setup(install_requires)?; Victor Stinner's pull request: "parse requirements in markers"
OpenStack Dependencies:
- mox: use mox3 or port tests on mock which works on Python 3 (mock has been integrated in Python 3.3 as unittest.mock)
- eventlet: not available on Python 3 yet, alternatives: asyncio (Tulip for Python 3.3+/Trollius for Python 2), Tornado
Portage in progress
- Oslo Messaging: Portage in Progress by Victor Stinner (dashboard)
- glanceclient: Portage in Progress by Cyril Roelandt (dashboard)
- heatclient: Portage in Progress by Cyril Roelandt (dashboard)
- neutronclient: Portage in Progress by Cyril Roelandt (dashboard)
- glanceclient: Portage in Progress by Cyril Roelandt (dashboard)
Portage done
- keystoneclient: Portage in Progress by Cyril Roelandt (dashboard)
Python 3 Status of OpenStack projects
See also Python3Deps.
OpenStack clients
Core OpenStack projects
Project | Python 3 compatibility | CI tests running? | Trove classifiers | Blocked by | Comment |
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ceilometer | No | No | No |
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cinder | No | No | No |
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glance | No | No | No |
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heat | No | No | No |
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horizon | No | No | No |
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keystone | No | No | No |
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neutron | No | No | No |
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nova | No | No | No |
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swift | No | No | No |
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